Graduate Student Researcher, University of California, Los Angeles
Using computers, I simulate liquid metal flowing in a magnetic field to help design fusion reactors
Fusion power generation is a popular choice for humanity’s ultimate power source because fusion is clean, safe, and sustainable. Fusion power reactors create heat by fusing hydrogen plasma at extremely high temperature and pressure. Such hot plasma would destroy the reactor’s walls except that the plasma is suspended inside the core of the reactor vessel by a very strong magnetic field. In some reactor designs, liquid metal lead-lithium (PbLi) is circulated to carry heat away from the reactor. The heat is then used for electrical power generation. Liquid metal PbLi is advantageous over other fluids because PbLi reacts favorably with neutrons from the fusion reaction; lead is a neutron multiplier and lithium reacts with neutrons to produce fuel for the reactor, tritium. However, because PbLi both flows inside the reactor's strong magnetic field and is a conductor of electricity, electromagnetic force acts on the liquid metal. Thus, the flow is governed by Maxwell's equations in addition to the usual conservation equations for mass and momentum. Such a flow is said to be a magnetohydrodynamic (MHD) flow. Using powerful computers, researchers simulate MHD flows to characterize the behavior of liquid metals flowing in conditions relevant to fusion power reactors. By uncovering the physics of MHD duct flows, researchers hope to inform fusion reactor designers and help bring the dream of fusion power to reality.
Abstract: One way of realizing controlled nuclear fusion reactions for the production of energy involves confining a hot plasma in a magnetic field. Here, the physics of magnetic-confinement fusion is reviewed, focusing on the tokamak and stellarator concepts.
Pub.: 03 May '16, Pinned: 29 Jun '17
Abstract: This is the final report of a panel set up by the U.S. Department of Energy (DOE) Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter dated September 10, 2002 from Dr. Ray Orbach, Director of the DOE's Office of Science. In that letter, Dr. Orbach asked FESAC to develop a plan with the end goal of the start of operation of a demonstration power plant in approximately 35 years. This report, submitted March 5, 2003, presents such a plan, leading to commercial application of fusion energy by mid-century. The plan is derived from the necessary features of a demonstration fusion power plant and from the time scale defined by President Bush. It identifies critical milestones, key decision points, needed major facilities and required budgets. The report also responds to a request from DOE to FESAC to describe what new or upgraded fusion facilities will “best serve our purposes” over a time frame of the next twenty years.
Pub.: 01 Jun '02, Pinned: 28 Jun '17
Abstract: In October 2003, Dr. Raymond Orbach, Director of the Department of Energy’s Office of Science, issued a charge to the Fusion Energy Sciences Advisory Committee (FESAC) “to identify the major science and technology issues that need to be addressed, recommend how to organize campaigns to address these issues, and recommend the priority order for these campaigns.” The sections in this report document the results of the Panel’s work. The first two sections describe the concepts of the overarching themes, topical scientific questions, and campaigns. The next six sections (Sections 3–8) describe in detail the six scientific campaigns. Section 9 describes some important enabling research activities necessary for the campaigns. Sections 10–12 describe the overarching themes, which provide a crosscutting perspective of the activities in the six campaigns. Finally, the Panel’s recommendations are set forth in Section 13. The charge letter to the panel is provided as Appendix A; the FESAC response letter is provided as Appendix D.
Pub.: 01 Jun '05, Pinned: 28 Jun '17
Abstract: Followed by a review of previous studies of magnetohydrodynamic (MHD) duct flows in a non-uniform magnetic field at the entry into a magnet (fringing magnetic field), the associated MHD problem is revisited for a particular case of a nonconducting rectangular duct of a small aspect ratio ε = b/a (here, b is the duct half-width in the magnetic field direction, and a is the half-height). The suggested model includes a realistic three-component div- and curl-free fringing magnetic field as well as inertia terms and takes into account the mechanism of electric current exchange between the core of the flow and the Hartmann layers. The original three-dimensional flow equations are reduced to a quasi-two-dimensional (Q2D) form for three basic scalar quantities: the vorticity, the streamfunction and the electric potential. This Q2 D formulation implies that the velocity field in the core region between the two Hartmann layers does not change in the magnetic field direction and thus is two-dimensional, while the induced electric current forms both cross-sectional and axial circuits and is essentially three-dimensional. A new parameter R = ε2Re/Ha has been identified to characterize the role of inertia in duct flows with insulating walls (Re and Ha stand for the Reynolds and Hartmann numbers). Computations and analytical studies are performed for inertialess (R ≪ 1) and inertial (R ≫ 1) flows at ε = 0.2 for Re up to 300,000 resulting in new scaling laws for typical lengths, velocities, electric current densities and pressure drops, which provide a new theoretical basis for potential applications.PACS Codes: 47.65.-d, 47, 47.11.-j
Pub.: 01 Oct '10, Pinned: 28 Jun '17
Abstract: Most numerical analysis performed in the past for MHD flows in liquid-metal blankets were based on the assumption of low magnetic Reynolds number and involved numerical codes that utilized electric potential as the main electromagnetic variable. One limitation of this approach is that such codes cannot be applied to truly unsteady processes, for example, MHD flows of liquid-metal breeder/coolant during unsteady events in plasma, such as major plasma disruptions, edge-localized modes and vertical displacements, when changes in plasmas occur at millisecond timescales. Our newly developed code MOONS (Magnetohydrodynamic Object-Oriented Numerical Solver) uses the magnetic field as the main electromagnetic variable to relax the limitations of the low magnetic Reynolds number approximation for more realistic fusion reactor environments. The new code, written in Fortran, implements a 3D finite-difference method and is capable of simulating multi-material domains. The constrained transport method was implemented to evolve the magnetic field in time and assure that the magnetic field remains solenoidal within machine accuracy at every time step. Various verification tests have been performed including purely hydrodynamic flows and MHD flows at low and finite magnetic Reynolds numbers. Test results have demonstrated very good accuracy against known analytic solutions and other numerical data.
Pub.: 05 Apr '16, Pinned: 28 Jun '17